Although numerous compounds are known to have medically useful effects on the cardiovascular system, hitherto there have not existed satisfactory agents which modulate the action of the sino-atrial node in warm-blooded animals such as man in a beneficial, selective and medically useful manner so that the agents are useful in treating cardiovascular disorders associated with an inappropriately elevated heart rate (that is by having a bradycardic effect) and yet have minimal effects on other haemodynamic parameters such as blood pressure or cardiac output. It is an object of the invention to provide such an agent which has inter alia bradycardic properties.
Pyrimidine derivatives have been extensively studied in the search for new pharmacologically active agents. A series of aminopyrimidine derivatives has been described as having cardiotonic properties (U.S. patent application Ser. No. 4,725,600). Various 4-aminopyrimidinium salts have been described as antifungal and anti-bacterial agents (U.S. patent application Ser. No. 4,339,453). The present invention is based on the unexpected and beneficial sino-atrial node modulatory effects of a novel series of a aminopyrimidine derivatives of formula I defined below.